What is the difference between partly sunny and partly cloudy?

Reposted from the Cliff Mass Weather Blog

Twice today I was asked about the difference between partly cloudy and partly sunny.   And that inquiry is one of the most frequent I get, for reasons I do not understand.

OK…let’s settle this for once and for all.

Here is an image of a partly cloudy sky:

And here is an image of a partly sunny sky:

They are the same.…. during the day, partly cloudy and partly sunny denote exactly the same thing:  a sky with between 3/8 and 5/8 coverage of clouds.   Obviously, partly cloudy would be a better choice at night.

Mostly cloudy  is 5/8 to 7/8 coverage, while mostly sunny indicates 1/8 to 3/8 coverage during the day.

Now, a harder one.   What does it mean to have a sky obscured?   Is it the same as an overcast sky?

The answer to the second question is NO–they are not the same.

The sky is obscured when you can not see the sky, when you are in middle of cloud or smoke or dust storm.  Here are two examples of an obscured sky, one from smoke and the other from low clouds/fog:

An overcast sky is when the entire sky is covered by clouds or smoke, but you are not in them.  You can see the base (bottom part) of the clouds or smoke.  Here is an example:

With this knowledge, you can amaze your friends at the next cocktail party…. whenever cocktail parties start again. 

97 thoughts on “What is the difference between partly sunny and partly cloudy?

  1. People will be “cootie conscious” for months, paranoid. I am near Detroit, and 4 years ago I got what I think was viral bronchitis from kissing a woman who brought it back from Istanbul a month earlier, she had no symptoms. Ya gonna get sick once in a while.

    • An optimist and a pessimist the difference is quite droll,
      the optimist sees the donut,
      the pessimist sees the hole.

    • Partly sunny vs partly cloudy. Glass half full vs glass half empty. Pessimist vs Optimist. Meh. All are “Six of one and half a dozen of the other.”

      I’m a realist. A realist first wants to know what is in the glass, so his choices are informed by real data.

      • ” Glass half full vs glass half empty”

        Engineers say “the glass is twice as big as it needs to be …”
        😉

        • I just say that you can refill the glass, so who cares. Works especially well with beer, wine and whisky in my experience 🙂

        • Engineers say “the glass is twice as big as it needs to be …

          A mechanical engineer would say the glass is overspecified.
          A chemical engineer would say that the glass really is full, it’s just two-phase.

          • The glass is intended to hold liquid, so it is not full (and the ChemE should be quiet)

            The glass is not over specified, is is intended to hold varying amounts; at this point in time it is at 50% capacity (and the ME should hire someone to help him see the bigger picture)

            A government PLANNER, on the other hand, says they have to rely on others to make their decision; they require the civil engineer has to submit a report, accompanied by an application describing the glass type, color, size, the location of the specific glass and any other nearby glasses (or similar containers), the intended use of the specific glass & the existing use of the nearby glasses, the liquid material contained in the glass, ownership of the glass (and whether or not the owner owns any adjacent glasses or containers) and “any other pertinent information”, along with the appropriate review fee for planning review and conditional approval. The application will then be reviewed to determine its ‘completeness’ before it is deemed incomplete and returned exactly 30 days later for corrections (e.g. “the glass is blue-green, not greenish with a blue hue”). With corrections, the planner will send the information out to interested parties for their comments and then after reviewing the comments state that, the glass has a substance in it that is appears to be liquid (but since an interested party has has hired a ChemE to dispute any approval, and has threatened to appeal any straight forward decision) they will need additional information … a computer generated report with a minimum thickness of 5/8″ thick should suffice. When the thick documents are received & filed (not necessarily reviewed) the planner will send out a billing for the additional review time (over & above the fee). By the time the planner has finished his conditional approval, the liquid has evaporated and any further discussion will need an new application (since conditions have changed).

        • >>
          Engineers say . . . .
          <<

          That’s what a non-engineer thinks engineers would say. To an engineer (such as myself), the glass size is correctly designed with an appropriate safety margin to prevent overflow.

          Jim

  2. Thanks Cliff.
    Now that those things have been cleared up, why is the planet’s ECS postulated to be 1.5C to 4.5C?
    Surely after ~40 years of research, and more CO2 in the air, we could be told a more precise range?

    • Climate alarmists say ECS is 3C to 5C/[2 x CO2] based on no credible evidence, because they need ECS to be that high to allege false alarm, aka “We’re all gonna burn!!! Be very frightened!!!”

      Climate realists calculate maximum ECS based on credible evidence to equal 1.0 to 1.5C, which is not alarming, aka “No sweat! Chill!” 🙂

      ECS is based on the assumption that increasing atmospheric CO2 drives warmer atmospheric temperatures. Since CO2 changes lag temperature changes by ~9 months in the modern data record, it may very well be that ECS does not even exist in physical reality.

      If this confuses you, think about a cart pulling a horse, and how you would define horsepower in this case. Same problem.

      • Allan, if I came across a cart pulling a horse, I wouldn’t be trying to figure out a horsepower rating.

        I’d be more worried about what was in that beer I just drank that gave me such visions.

        • Both sides of the climate debate have been drinking magnums of the same over-proof rum for decades, and have spent their time arguing about the magnitude of ECS (and TCS) as if it actually exists.

          There is significant evidence that ECS/TCS is an imaginary concept that does not exist in reality, but is a fiction – a result of long-term alcohol abuse, an apparition caused by a bad case of the DTs.

          If one focuses on periods of observed global warming (e.g. 1979 to 2017) one can calculate a hypothetical ECS value of approx. 1C/(2*CO2).

          If one focuses on periods of observed global cooling (e.g. 1940 to 1977), one can calculate a hypothetical ECS value of approx. MINUS 1C/(2*CO2).

          Both hypothetical values of ECS are too low to cause alarm – end of the very-scary global warming (CAGW)/climate-change story – a satisfactory result, as far as it goes..

          But scientifically, atmospheric CO2 changes lag atmospheric temperature changes at all measured time scales, from ~9 months in the modern data record to ~~800 years in the ice core record – aka “cart before horse”.

          Kuo et al (1990) and Keeling (1995) both observed that “CO2 changes lagged temperature changes” in the modern data record. That reality has been studiously ignored in the current climate debate. I independently re-discovered that observation (temperature changes lead, CO2 changes lag) in January 2008 and have provided the details of the physical mechanism in papers published from January 2008 to June 2019.

          That observation does not preclude other sources of increasing atmospheric CO2 such as fossil fuel combustion, deforestation, etc. but it does provide further evidence that THE ENTIRE GLOBAL WARMING/CLIMATE CHANGE STORY IS A SCARY FICTION, FOR WHICH THERE IS NO CREDIBLE EVIDENCE.

          CO2, GLOBAL WARMING, CLIMATE AND ENERGY
          by Allan M.R. MacRae, B.A.Sc., M.Eng., June 15, 2019
          https://wattsupwiththat.com/2019/06/15/co2-global-warming-climate-and-energy-2/
          Excel: https://wattsupwiththat.com/wp-content/uploads/2019/07/Rev_CO2-Global-Warming-Climate-and-Energy-June2019-FINAL.xlsx

        • I was driving the interstate the other day and saw a cart pulling a horse. And I don’t even drink alchohaul.

      • As far as the cart pulling the horse the horsepower would remain the same. Either the hill is too steep to climb or the traction is poor.

        • I guess to be clear I should have noted that I considered that the cart was dragging the horse backwards down the hill.

          Maybe I should also note that I was being a smartass!

      • You must also consider your perception of the horse and the cart. Maybe the horse was pushing the cart! Still one horsepower but perhaps more reliable if the cart had carrots!

        • If the cart was pulling the horse, then the horsepower would be an imaginary number – like ECS – visible only to those with a bad case of the DTs. 🙂

          Post Script:
          For those who rush to tell me that an imaginary number is a product of a real number times the square root of minus one: Yeah, I knew that.

  3. “Tonights forecast is dark. Continuing dark throughout the night, with widely scattered light in the morning.”
    — The Hippy Dippy Weatherman, George Carlin

  4. @Cliff – For the next weather trivia, please do “chance of rain.” (Keep on having to explain to people that “50%” does not mean it will rain right here for half the day. Especially right here – some monsoon seasons, my neighborhood seems to have a rain shield around it…)

    • Yeah, I have a problem with that. Is it chance of rain anywhere in the specified region, chance of rain at any particular place in the region, etc?

  5. When I was an Air Traffic Control Tower Operator trainee, in 1968, at Lowe Army Airfield, Ft. Rucker, Alabama, we had a morning of: W0X0F (W-zero-X-zero-F). This was sky obscured, zero vertical visibility, zero visibility, fog. We could not see the ground from the tower, Then a helicopter starts up, in comes an IFR flight plan, with the pilot properly instrument certified, he calls, is cautioned about W0X0F, and takes off. Heard the sound but never saw him.

    • Travelling in a helicopter in Seattle in exactly such weather, the pilot saw the top of a building with someone enjoying a sneaky smoke. He hovered over the building and called out to the smoker, asking where he was. The smoker replied “in a helicopter”.

      The pilot thanked the smoker, and found his way to the airport. On exiting the helicopter, a passenger asked the pilot how he could find his location from such a useless reply. He said:

      “That’s easy, I knew I was above the Microsoft Support Center”.

      “But how could you know that?”

      “Well, the information the smoker gave me was completely accurate, but utterly useless!”

    • My favorite is CAVU.

      It is indeed possible to take off and land in zero zero. The fire trucks won’t be able to find you if you crash though. (unless things have changed in the last thirty years)

    • That’s very good.
      An old comedy skit I remember (Australian) dealt with a new product, “Crack Spackle”, used to fill in the large fissures exposed, when working, by plumbers, carpenters and others of that sort.

      • Not to be confused with ‘plumbers crack’. 🙂 There is a product on the market here called Spack Filler!

  6. If they are the same why are they different?

    Seriously this is the kind of triviality that annoys the crap out of people. Not that Partly Sunny is the same as Partly Cloudy, but rather that there are over educated wetwipes who revel at knowing this nonsense and correcting people that don’t.

    • Wlm,
      As the FAA defines cloud coverage;
      few = 1/8 – 2/8 ths of the sky
      scattered = 3/8- 4/8
      broken = 5/8 – 7/8
      overcast = 8/8

      Pilots care mainly about the overcast layer and the altitude of the bases. We can fly around all the other clouds…usually.

      • The amount of cloud cover also determines the official “ceiling”. You can have a scattered layer, another scattered layer and a broken layer. The broken layer would be the actual ceiling. Also cloud coverage is expressed in okta’s (which is what JimH is posting). 1 okta is 1/8th coverage but to confuse things a bit, there is a 9 okta which is an indication of an obscured sky.

  7. My late father was, before he retired, the top instrument rated prop pilot (he did not transition to jets) in the USAF. He was also sent by USAF to UCLA for two masters degrees in 1946. One in meteorology, and one in electronics (Weather radar). Then flew weather recon for three years off Guam as Commander of the 409th typhoon chasers squadron using modified B-29 aircraft (Bombays converted to lots of radar instrumentation and dropsondes). Very earliest serious tropical storm/typhoon research in the Pacific.

    He used to tell weather jokes like Cliff’s partly cloudy/partly sunny nondifference around the dinner table. A feeble but fond memory example follows.

    All a meteorologist really needs to diagnose present weather is a good weather string.
    If you can see its shadow, its sunny.
    If you cannot see its shadow, its cloudy.
    If you cannot see it at all in daytime, its foggy.
    If it isn’t hanging vertically, its windy.
    If it is wet, its raining.
    And so on.

    Then he would say—Diagnose the weather for tomorrow is much more difficult. Strings won’t help.

      • When I was young people used to hang a strip of seaweed outside their back door.
        If it was damp it would rain, if dry it would be fine, ( and if you couldn’t see it it was foggy).
        The only thing it might forecast accurately is the relative humidity due the salt in the seaweed attracting moisture.

    • We had a weather rock. Basically the same thing (wet=rain, white=snow, etc). If it was gone, it meant a tornado.

  8. When I was living in Buffalo, NY, a common weather forecast was for “a mix of sun and clouds.” And true enough, it was a hazy day. Take the top two pictures in this post and stir.

    Buffalo has never been known for nice weather.

  9. Partly sunny is with a cloud bias. Partly cloudy is with a sun bias. Each approaches a limit from a different starting point.

  10. The partly sunny became popular back in the early 1970s, as best I recall. Some busybody weather personality decided partly sunny was more cheery that partly cloudy. All the meteorologists I knew at the time kept on with the usual partly cloudy line, but not so the radio/TV personalities.

  11. Partly cloudy…partly sunny. That reminds me of the story of the Indian Chief visiting London for a University conference on Language. The words being discussed were Complete and Finish. All the professors and experts agreed the meaning of the two words were essentially the same, and even the dictionary says as much.

    The wise old Indian Chief stood up, spoke and said; When you have a good woman you are complete. When you have the wrong women, you are finished. And when the right woman catches you with the wrong woman, you are completely finished!

  12. During the Second World War radio announcers could not talk about the weather. So when the base ball game was rained out the announcer said, “Folks, the game has been cancelled. I can’t tell you why, but if you stick your head out the window, you’ll figure it out.”

  13. Cliff,
    so far in the comments we have had optimist, cliff and low cloud.
    so here is my story, combining all three.:)

    In the late 70s, I was a soldier on the tiny island of st Kilda,50 miles off the outer Hebrides in Scotland. one day I wandered out of the radar station for a stroll along the 600 feet cliffs and a cloud, or mist , or fog came down and I was stuck. all I could hear were the crashing waves, I could barely see my hand in front of my face. I was feet from the cliffs edge and I was completely disorientated.
    I sat down straight away. one false move and I was over the edge.
    Made a little circle of stones, like a clock face.
    Then I threw a pebble at 12 oclock. one oclock and so on.
    I moved towards 12 till one of the pebbles made no sound. the cliff edge. moved in the opposite direction and eventually the pebble hit a wall. I was saved. there are lots of pebbles on that island

  14. I think that to the average person simply reacting to the words, partly cloudy would imply sunny with some clouds, and partly sunny would imply cloudy with some sun. Although they are the same, the connotation is that one would have more sun than the other.

  15. More interesting might be the basic question, what the relation between cloudiness and temperature is. Is it warmer with or without clouds? A question of fundamental importance to all climate “science”, which every weather guy should easily be able to answer.

    Spoiler alert! I checked it out for myself, here with the example of the Aleut Islands, where according to NASA cloud forcing is meant to be massively negative.

    Seasonally resolved:
    https://www.climate-debate.com/forum/attachments/aleuten1.png

    Annual average:
    https://www.climate-debate.com/forum/attachments/aleuten2.png

  16. I’ve always felt that Partly Sunny was the same as Mostly Cloudy, and that Partly Cloudy was the same as Mostly Sunny. I don’t see Partly Sunny and Partly Cloudy as the same at all.

  17. Pay attention because the weather forecast is going to change, often and at short intervals.

    But climate models can tell us what the weather is going to be like 50 years from now /sarc

  18. A friend once phoned me up and asked if I knew what the weather was doing.
    I told her – “looks like scattered small clouds borne on a gentle Easterly breeze and mild to warm”
    She said – “oh, that sounds perfect, what weather site are you looking at?”
    I said – “it’s the SYHOTFW site”
    She said – “is that .com or .com.au?”
    I said – “Neither. It means Stick Your Head Out The F’n Window”

  19. “An overcast sky is when the entire sky is covered by clouds or smoke, but you are not in them.”

    I always thought an overcast sky was a cloudy sky. Apparently, smoke can also cause an overcast sky if it is high up and you are not in the smoke. Good to know, I guess.

  20. If you live anywhere in the soggy parts of the Pacific Northwest (like Western Washington and Oregon), then partly sunny is what everyone else would call partly cloudy.

  21. I disagree.
    The sky can be Partly Cloudy without having a single minute of cloud covering the sun.
    If the sky is Partly Sunny that means there are times when the sun is blocked.

    Partly sunny has less minutes of sunshine than partly cloudy

  22. I honestly thought this post would lead to a much more boisterous discussion.

    Sort of like a conversation Rorschach Test.

  23. Partly Cloudy: A term used by negative thinking liberals.

    Partly Sunny: A term used by optimistic conservatives who never whine over that half glass of spilled milk.

  24. I’ve been wondering the same thing for years! Partly cloudy is the same thing as partly sunny!!! But weather people ALWAYS say partly cloudy. Why? Partly sunny gives you more optimism. And it’s the same weather forecast! It’s like saying “you only have 1/2 a tank of gas.” Makes it sound negative like you’re in peril. But if you say ” you have 1/2 a tank of gas.” By not using only it makes it more positive. You’re not going to run out of gas with 1/2 a tank unless you’re in Chicago and live in Miami. Just choice of word(s) that gives same phrase a whole different meaning. Weird. But yet weather people never seem to get it! As above “I get asked this question all the time.” Duh! Do you get it now?!

  25. Now that you cleared that up, what is the differance between scatered showers and a 10, 30 30 40 50% chanch of rain?

  26. My favorite weather report phrase often heard in the Pacific Northwest is “overcast with a possibility of sun breaks”.

  27. As a former operational weather forecaster, I never thought that partly sunny and partly cloudy were equivalent. As Edward Joseph Tiegs wrote above, partly sunny should denote less sun than partly cloudy through the day.

    And now for a brief rant: with the advent of ASOS in the 1990s, younger meteorologists generally do not have the atmospheric observational training and capability of meteorologists of yore. Back in the days before ASOS, when a Weather Observer took an observation the whole hemisphere of the sky was observed, and lots of detail was noted, often useful to an analyst or forecaster. The “bright brains” around 1990 decided that nothing of import happened above 12 thousand feet anyway. I believe this has been a loss of knowledge about atmospheric observations from one generation to the next, and this is not a good thing. At one time, ASOS was thought to be a gap-filler type of observational platform, but then the bureaucrats became involved and the rest is history.

    A old (sexist?) definition of a meteorologist: a meteorologist is a guy who can take one look at a girl and tell whether.

  28. Rexx Shelton, scattered showers means 30% to 50% coverage. An isolated shower is 20% coverage, numerous (or likely) refers to 60-70%, and widespread (or occasional) is 80-100%.

  29. I always thought that “partly cloudy” means that it’s slightly more cloudy than “partly sunny”, and “partly sunny” means that it’s slightly more sunny than “partly cloudy.” Clear enough, eh? 😉

  30. ‘Partly sunny’ means you might be lucky enough to get a short period when the sun shines down between the clouds, before it becomes obscured again.

    ‘Partly cloudy’ means an occasional cloud might obscure the sunshine you’re enjoying, before said cloud passes and the sunshine resumes.

    They don’t mean the same thing.

  31. “And that inquiry is one of the most frequent I get, for reasons I do not understand.”

    Yeah, gotta ask if you get more of these in the spring than any other time, ’cause I’m pretty sure this question is asked in every garden center, every year…

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